Ancient oxygen discovery shakes up history of life on Earth

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Oxygen appeared in the Earth’s atmosphere up to 700 million years earlier than thought, according to a study led by a B.C. scientist, suggesting that revisions need to be made to current theories about how life evolved on Earth.

Up until now, scientists thought photosynthesis — the ability of living things such as algae and plants to harvest energy from the sun  — first evolved in single-celled organisms about 2.7 billion years ago.

Because oxygen is produced during photosynthesis, early photosynthetic organisms are thought to have given rise to the Great Oxygenation Event, also known as the Great Oxidation, about 2.3 billion years ago.

The incident was thought to be the first time the atmosphere began accumulating significant amounts of oxygen. That is significant because complex multicellular organisms such as humans require an oxygen-rich atmosphere to survive.

The new study led by biogeochemist Sean Crowe has found surprising evidence that as far back as three billion year ago, there were levels of oxygen in the atmosphere too high to have been produced without living organisms.

Written By: Emily Chung
continue to source article at cbc.ca

7 COMMENTS

  1. Oxygen appeared in the Earth’s atmosphere up to 700 million years earlier than thought, according to a study led by a B.C. scientist, suggesting that revisions need to be made to current theories about how life evolved on Earth.

    There are other ways for free oxygen to be produced on planets, which they mention, but do not explain the basis of their calculations.

    http://scitechdaily.com/earth-loses-50000-tonnes-of-mass-every-year/

    The Earth’s core loses energy, since much of it is consumed in a planet’s lifespan, but that only accounts for a loss for about 16 tonnes per year. The biggest mass loss comes from escaped hydrogen and helium, which escape with 95,000 tonnes of mass and 1,600 tonnes respectively. These elements are too light to stay permanently in the gravity well, so they tend to escape into space.

    The net loss is about 0.000000000000001% every year, so it doesn’t account for much when compared to the total mass of the Earth, which is 5,972,000,000,000,000,000,000 tonnes. It will take trillions of years for all of the hydrogen to be depleted. Helium represents 0.00052% of the atmosphere and it’s a scarcer element.

    This hydrogen is liberated from the dissociation of water molecules in the upper atmosphere by solar radiation, leaving their oxygen atoms/molecules behind.

    Of course in the atmosphere of the early Earth there were initially readily oxidizable gasses as there are in the atmospheres of planets of the outer solar system today, so any “freed oxygen” would quickly react with the molecules around it.

    It would seem that around 3.9 billion years ago there was an extensive period of impacts ( the late heavy bombardment) from comets carrying material from the outer Solar System

    There was also much iron dissolved in the seas and sulphur from hydrothermal vents, which would react with any oxygen reaching sea level.

    Nevertheless, the persistent degradation of the anoxic atmosphere by solar radiation with intermittent top-ups of outer solar system gases from comets/asteroids, could leave the possibility of some oxygen from solar dissociation of water molecules, reaching the ground at some times.

    @OP link – But computer modelling showed that the oxygen levels three billion years ago were still five times higher than the amount that could be generated by chemical reactions in the atmosphere alone, without the help of photosynthesizing living organisms.

    “Once … we realized there’s really a lot more oxygen than you can produce abiotically, we were very excited,” Crowe said.

    “Because we capture oxygen in the atmosphere three billion years ago, the likelihood is that oxygen-producing organisms evolved before that — very early in Earth’s history.”

    The first life is thought to have formed on Earth about 3.8 to 3.5 billion years ago, shortly after the Earth became cool enough to form oceans and continents.

    The link does not explain what basis they used for measuring or estimating the ” abiotically produced oxygen”, or what else may have been absorbing it or releasing it, so it is difficult to evaluate their claims.

    I also have to wonder, given the massive impact craters around 3.9 billion years ago, if their oxidised forms of chromium that only occur following reaction with oxygen, might have formed locally from dust in the upper atmosphere where the abiotic oxygen was being produced.

    There is a similar BBC report on the present weight of the Earth here; Who, What, Why: Is the Earth getting lighter?- http://www.bbc.co.uk/news/magazine-16787636

    • In reply to #2 by Alan4discussion:

      I agree, there are lots of ways for chromium to oxidise, and there’s no shortage of atmospheric and geological chemistry 3 billion years ago. Also all the samples appear only to come from one South African source – so it seems a bit early to be shouting the odds.

  2. I get so annoyed when popular (i.e. non-scientific) news sources announce that science as been “shaken up” or “overturned” or “proven wrong” by some new discovery. There always seems to be a note of anti-science-Schadenfreude in the announcement, as if it were once again a proof that you can’t trust the men in the lab coats. They never make any mention to the ongoing refinement and self-adjustment process that goes on in the scientific method itself. Just those stupid gleeful little remarks.

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